This invention relates to improvements in a temperature measuring system having temperature sensing means of the type which performs a temperature-to-frequency or temperature-to-period conversion through use of a CR oscillator circuit wherein a thermistor is included in the resistance for forming the CR-time constant, the oscillation frequency of the oscillator circuit varying with a change in ambient temperature. The invention relates also to a temperature compensating system, used in an electronic timepiece, whereby a time base signal produced by crystal-controlled oscillator circuit is subjected to temperature compensation on the basis of temperature data acquired from the improved temperature measuring system.
A well-known method of sensing a change in ambient temperature relies upon a CR oscillator (namely an oscillator which includes capacitance and resistance elements forming a time constant) in which a thermistor forms all or a part of the oscillator time-constant resistance. The arrangement is such that the change in temperature is sensed on the basis of a change in the oscillation frequency of the CR oscillator, caused by a variation in the thermistor resistance. This method has found wide application in a variety of digital measuring instruments since it is the most simple means of digitally quantifying analog environmental temperature information. However, since the magnitude of the thermistor resistance varies exponentially with respect to a change in temperature, as will be described in further detail below, the oscillation frequency and period of the CR oscillator also are exponential functions of the temperature, so that temperature data which varies linearly with respect to temperature cannot be obtained. This leads to a number of difficulties. For example, temperature data in the form of an exponential function cannot be utilized directly to provide a visual display of temperature. Moreover, in electronic devices of the type in which temperature compensation is essential, problems are experienced in compensating for a temperature-induced error term which varies proportionally with respect to temperature.
A further difficulty is that a very large difference develops between the oscillation frequency at low temperature and the oscillation frequency at high temperature when temperature is measured over a broad range of values or when, based upon such a temperature measurement, compensation is effected over a greater range in an electronic device such as an electronic timepiece. This necessitates a large amount of counter circuitry for the analog-to-digital conversion. To improve upon these defects, it has been proposed to combine the thermistor with a number of series- and parallel-connected resistors so that the change in the combined resistance will be approximately proportional to the change in temperature over a certain temperature range, or so that the change in combined resistance may be expressed as a specific function. However, the temperature characteristics of the combined resistance expressed in this fashion are all approximate characteristics, and there are many functions which are impossible to realize. Another disadvantage is that the combined resistors are large in number and must have resistance values that are highly accurate, thereby raising the cost of the temperature measuring device by a wide margin.